To identify unknown genetic loci determining alcoholism, we are testing for linkage or association between genetic markers and behavioral phenotypes. The probability of establishing linkage or association is being maximized by 1) focusing on alcoholism with impulsivity/aggressivity as a prominent accompanying behavioral trait, 2) utilizing mouse genetic models, 3) using very large panels of DNA and protein polymorphisms and 4) studying in detail candidate genetic loci including tryptophan hydroxylase, the alcohol dehydrogenases and Y chromosome loci. Human linkage markers include 390 DNA probes of which we are currently typing 100 and also include more than 50 polymorphic proteins detectable by two dimensional protein electrophoresis (2DE). These polymorphisms are being typed in two large families with alcoholism. In the mouse, we identified 14 brain polypeptide variants and preliminarily mapped a locus for alcohol preference to chromosome 1. We cloned, sequenced and analyzed the expression of human Class III alcohol dehydrogenase. We detected a Sac 1 RFLP for Class III ADH and established that it is Class III HDH in a wide variety of tissues and in the fetus with a constant message size. We are determining whether Class III ADH is part of the ADH gene complex which we have demonstrated is present on Chromosome 4. We have cloned, sequenced and analyzed the expression of a mouse mastocytoma tryptophan hydroxylase.